This appears to be a very good idea for battery storage for the Outbacks, a problem that for a long time hasn't had a good answer or solution. But once again with human ingenuity, this turned out pretty neat, confined and protected in a hatch.
You may want one or two of these, or you may not. Take a look and decide. I ended up buying two.
The man making this box makes them by himself apparently. He says he runs out, but makes more as fast as he can or gets the time, so if you want one and they aren't listed or on this link, do a search using "Kayak Battery & Storage Box Fits Hobie 8" round Hatch" or something similar as your search phrase.